Objective:To characterize the minimal inhibitory concentration (MIC) of macrolides against clinical Mycoplasma pneumoniae (MP) isolates and to investigate the significance of 23S rRNA mutations. Methods:Cross-sectional study.A total of 288 clinical MP strains preserved in the laboratory from 2016 to 2021 were taken for macrolide resistance gene testing and the evaluation of in vitro susceptibility to Azithromycin and Erythromycin.MIC 50 and MIC 90 values were calculated separately for macrolide-susceptible and -resistant strains. Results:All 288 MP strains underwent the test of in vitro susceptibility to Azithromycin, while 86 of them were additionally tested for Erythromycin.Among these strains, 22 strains were Azithromycin-sensitive, and 266 strains were Azithromycin-resistant.A2063G mutations were detected in 260 (97.7%) strains, while A2064G mutations were detected in 6 (2.3%) strains.Azithromycin-resistant strains had an MIC 50 of 128.000 μg/mL and an MIC 90 of 512.000 μg/mL, with the MIC ranging between 16.000 and 512.000 μg/mL.Seven strains were sensitive and 79 strains were resistant to Erythromycin.Among Erythromycin-resistant strains, A2063G mutations were detected in 73 (92.4%) strains, while A2064G mutations were detected in 6 (7.6%) strains.Erythromycin-resistant strains had an MIC 50 of 256.000 μg/mL and an MIC 90 of 512.000 μg/mL, with the MIC ranging between 64.000 and 1 024.000 μg/mL. Conclusions:A2063G and A2064G mutations in the 23S rRNA gene of MP are associated with high-level in vitro resistance to Azithromycin and Erythromycin, significantly limiting the clinical effectiveness of these antibiotics.Early resistance gene testing is recommended for suspected MP patients, which can help optimize the treatment, improve prognosis, and prevent resistance spread.

Objective:To characterize the minimal inhibitory concentration (MIC) of macrolides against clinical Mycoplasma pneumoniae (MP) isolates and to investigate the significance of 23S rRNA mutations. Methods:Cross-sectional study.A total of 288 clinical MP strains preserved in the laboratory from 2016 to 2021 were taken for macrolide resistance gene testing and the evaluation of in vitro susceptibility to Azithromycin and Erythromycin.MIC 50 and MIC 90 values were calculated separately for macrolide-susceptible and -resistant strains. Results:All 288 MP strains underwent the test of in vitro susceptibility to Azithromycin, while 86 of them were additionally tested for Erythromycin.Among these strains, 22 strains were Azithromycin-sensitive, and 266 strains were Azithromycin-resistant.A2063G mutations were detected in 260 (97.7%) strains, while A2064G mutations were detected in 6 (2.3%) strains.Azithromycin-resistant strains had an MIC 50 of 128.000 μg/mL and an MIC 90 of 512.000 μg/mL, with the MIC ranging between 16.000 and 512.000 μg/mL.Seven strains were sensitive and 79 strains were resistant to Erythromycin.Among Erythromycin-resistant strains, A2063G mutations were detected in 73 (92.4%) strains, while A2064G mutations were detected in 6 (7.6%) strains.Erythromycin-resistant strains had an MIC 50 of 256.000 μg/mL and an MIC 90 of 512.000 μg/mL, with the MIC ranging between 64.000 and 1 024.000 μg/mL. Conclusions:A2063G and A2064G mutations in the 23S rRNA gene of MP are associated with high-level in vitro resistance to Azithromycin and Erythromycin, significantly limiting the clinical effectiveness of these antibiotics.Early resistance gene testing is recommended for suspected MP patients, which can help optimize the treatment, improve prognosis, and prevent resistance spread.

Objective:To investigate drug resistance gene in Mycoplasma pneumoniae(MP) and the distribution of 13 respiratory pathogens in bronchoalveolar lavage fluid(BALF) of children with Mycoplasma pneumoniae pneumonia(MPP).Methods:A total of 100 BALF of children with MPP in Peking University Third Hospital and Peking University First Hospital from January 2018 to January 2019 were collected.Fluorogenic quantitative PCR was used to detect nucleic acid and it′s drug resistance gene of MP and multiple PCR method was adopted to detect influenza A virus, influenza A virus-H 1N 1, influenza A virus-H 3N 2, influenza B, human parainfluenza virus, adenovirus, human bocavirus, human rhinovirus, Chlamydia pneumoniae, human metapneumovirus, MP, human coronavirus, and respi-ratory syncytial virus gene, and the results were compared by using Chi square test. Results:In 100 BALF samples, MP and drug resistance gene were detected by fluorogenic quantitative PCR.Totally, 83 cases (83.00%) were MP positive and 78 cases (93.98%) were drug resistant.All of them had the point mutations A2063G in V region of 23S rRNA domain.A total of 13 kinds of respiratory pathogens were detected by multiplex PCR method, and 89 cases (89.00%) were positive.Totally, 79 cases (79.00%) were MP positive, of which 74 cases (74.00%) detected only MP, and 5 cases (5.00%) detected MP combined with other pathogens.Other pathogens were detected in 10 cases (10.00%). The virus detection rate of 0-4 years old group was higher than that of >4-6 years old group ( P=0.042) and >6 years old group ( P=0.002), and the differences were statistically significant. Conclusions:MP can be detected in most BALF samples of MPP children, the drug resistance phenomenon is serious, and the main point mutation is A2063G.There were other respiratory pathogens and 2 or 3 pathogens were detected in a small number of BALF samples.

Objective:To compare the laboratory diagnostic methods of Mycoplasma pneumonia(MP) and evaluate its clinical value.Methods:A prospective study.Throat swabs and double sera of children with MP infection were collected from December 2016 to January 2017 in Shengjing Hospital Affiliated to China Medical University; throat swab samples of healthy children aged 3 to 5 in Chaoyang District, Beijing were collected from March to May 2017.Passive agglutination (PA) was used to detect the double serum.Taking the 4-fold increase or decrease of the specific antibody titer of the double serum as the gold standard, the receiver operating characteristic curve (ROC) was drawn, and the laboratory methods for detecting MP infection were compared and evaluated.Results:(1)A total of 93 children with MP infection were clinically diagnosed, including 42 males (45.2%) and 51 females (54.8%), with an average age of 5.5 years.Sixty cases (64.5%) of MP infection were diagnosed.There were 349 healthy children, 198 males and 151 females, with an average age of 4.3 years.The positive rate of throat swab culture was 0.6% (2 cases), and the positive rate of fluorescent quantitative PCR(qPCR) was 18.9% (66 cases). (2) The culture specificity was the highest (100.0%) and the sensitivity was the lowest (65.0%). PA and enzyme linked immunosorbent assay (ELISA) were used to detect a single serum in the acute phase, the sensitivity was 71.7% and 86.5% respectively.ROC curve suggested that the current clinical diagnostic threshold MP specific antibody IgM ≥ 1∶160 was not the best diagnostic threshold.Molecular biological diagnostic methods were the most sensitive, RNA simultaneous and testing (SAT) was 85.0% and qPCR was 93.0%; while the specificity was low, 75.7% (SAT) and 63.6% (qPCR), respectively.(3) At the same time, MP nucleic acid (SAT, PCR) of throat swabs and a single serum (ELISA, PA) of children in acute phase were detected, the sensitivity was increased to 95.0%-100.0%, and the specificity was 63.6%-75.7%.Conclusions:Molecular biology is highly sensitive in diagnosing MP infection.It has asymptomatic infection or is carried after infection.Whether it needs treatment needs to be combined with clinical practice, when MP detection is positive.The detection of a single serum in the acute phase with a course of about 1 week has high sensitivity and is of reference value for the diagnosis of MP infection, but the diagnosis needs to be combined with clinical practice.The sensitivity and accuracy of detecting MP infection by single serological test combined with SAT in acute phase are higher than that by single application.

Objective:To understand the pathogen distribution of children with influenza in North China in the past 2018-2019 years, and compare the accuracy of influenza virus antigen test results with that of influenza virus nucleic acid test results, provide reference data for clinical use good influenza virus pathogen detection methods.Methods:Five hundred and eighty throat swab samples of influenza-like children in 10 hospitals, northern China, were collected from December 2018 to January 2019.Each sample was tested by rapid influenza diagnostic test and reverse-transcription polymerase chain reaction(RT-PCR).Results:Of all 580 clinical samples, 256 positive samples (256/580 cases, 44.14%)were detected by the influenza rapid influenza diagnostic test, of which 235 were pure influenza A(235/256 cases, 91.8%), 21 cases were pave influenza B(21/256 cases, 8.2%), and 324 case were negative samples(324/580 cases, 55.86%). No cases were detected positive A and B at the same time.Of all 580 samples were detected using the A /B influenza virus RT-PCR, and a total of 353 cases(353/580 cases, 60.9%) were positive (of which 242 cases were influenza virus antigen-positive), of which 311 were pure A influenza(311/353 cases, 88.1%) and 41 were pure B influenza(41/353 cases, 11.6%), 1 case of mixed infection of A and B(1/353 cases, 0.3%), and 227 cases were negative(227/580 cases, 39.1%). In 324 cases of influenza virus antigen negative samples, 111 cases(111/324 cases, 34.3%) were positive for influenza virus nucleic acid.The detection rate of influenza A in Taiyuan was 23.2% (22/95 cases), and the detection rate of influenza B was 43.2% (41/95 cases), which was significantly different from other regions.With reverse-transcription polymerase chain reaction detection as the standard, the diagnostic value of influenza pathogen detection reagents was evaluated.The sensitivity, specificity, missed diagnosis rate, misdiagnosis rate, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, Youden index and area under the receiver operating characteristic curve were 68.56%, 93.83%, 31.44%, 6.17%, 94.53%, 65.74%, 11.12, 0.335, 0.624 and 0.812.Conclusions:From December 2018 to January 2019, the majority of children′s influenza in northern China is influenza A virus.Except Taiyuan which is dominated by influenza B. Influenza virus nucleic acid detection has high sensitivity and specificity for diagnosing influenza, and also has the ability to distinguish virus subtypes.Influenza virus antigen detection has a certain diagnostic value, a good specificity (93.83%), sensitivity (68.56%) which needs to be further improved, and a certain rate of missed diagnosis (31.44%) needs to be paid attention to possible missed diagnosis.Detecting positive cases of influenza virus antigens should be given a fast and effective anti-viral treatment, while the negative cases, especially those at high risk for influenza complications, should be confirmed influenza virus RT-PCR as soon as practical.

Objective To investigate the antibacterial effect of Fusidic acid on Mycoplasma pneumoniae and antibiotic resistant Mycoplasma pneumoniae in vitro.Methods Twenty-eight clinical strains of Mycoplasma pneumoniae isolated from patients with respiratory tract infection at Beijing Friendship Hospital Affiliated to the Capital University of Medical Sciences from January to December 2016 and 2 Mycoplasma pneumoniae reference strains were enrolled.The minimum inhibitory concentration (MIC) of Fusidic acid and Azithromycin were determined by using micro-dilution ration method.The chessboard method was used to check the antibacterial effect of combination between Fusidic acid and Azithromycin.The antibacterial activity of the Fusidic acid was evaluated by measuring the antibacterial rate of different concentrations.Results One isolate showed no mutation in 23SrRNA,26 isolates had one point mutation in loci 2063 and 1 isolate had one point mutation in loci 2064 among the 28 clinical isolates.The findings by micro-dilution method results showed that the MIC values of all the clinical isolates with mutations associated with macrolide resistance to Azithromycin were ＞ 1.000 0 mg/L,and the MIC values of all the clinical isolates with no mutations to azithromycin were ＜ 0.500 0 mg/L.The findings by micro-dilution method results showed that the MIC value of Fusidic acid for Mycoplasma pneumonia and drug resistance Mycoplasma pneumoniae was 1.000 0 mg/L.The Fractional Inhibitory Concentration index of Fusidic acid and Azithromycin combination was ≤0.500 0 mg/L.When the concentration of the Fusidic acid was lower than or equal to 32 MIC,the antibacterial effect of Fusidic acid against Mycoplasma pneumoniae increased with its higher concentration.When the concentration of the Fusidic acid was lower than or equal to 8 MIC,the longer the strain was exposed to the drug,the stronger antibacterial effect was against Mycoplasma pneumoniae.Conclusion If the treatment of Mycoplasma pneumoniae infection is not effective or the infection of patient is combined with bacteria,the application or combination of Fusidic acid may inhibit pathogenic bacteria effectively.Of course,how to use Fusidic acid in clinical treatment needs further study and discussion.

Objective To developed A laboratory diagnosis of Moraxella catarrhalis by an laboratories diagnostic method real-time fluorescence quantitative PCR assay. Methods The specific primers and probes were designed based on the sequence of outer membrane protein CopB(copB)gene in Moraxella catarrhalis,and the Taqman probe RT-PCR method was developed to detect the Moraxella catarrhalis.The standard plasmids ex-tracted from the Moraxella catarrhalis standard strains were used to constitute the standard samples,and compared with these standard samples,the sensitivity of the fluorescence quantitative PCR assay was tested by the estab-lished standard curves.The specificity of the fluorescence quantitative PCR assay was tested by the DNA samples of other bacterias in the laboratory.Meanwhile,321 throat swab samples from inpatient and outpatient child pa-tients,with asthma infection were collected as clinical samples to validate the fluorescence quantitative PCR as-say.Results The standard curve was drawn in the real-time PCR by the Taqman fluorescence reporter.During the sensitivity tests,the newly-developed real-time fluorescence PCR could detect at least 10 copies of Moraxella catarrhalis,and could successfully distinguish several DNAs of the pathogens.On the basis of the validation result of the 321 throat swab samples,there are 25 Moraxella catarrhalis with 7.79 % positive rate.Conclusion The fluorescence quantitative PCR assay is of great sensitivity and specificity,and it can be widely used for the detec-tion of Moraxella catarrhalis.